The present invention relates to controlling movement of a piston in a metering device.
European Patent Application EP 87114091.9 relates to a pumping apparatus for delivering liquid at a high pressure, in particular for use in liquid chromatography. FIG. 12 shows a conventional liquid chromatography system 120, which comprises a pumping apparatus 121, a valve switch 127, a sample loop 126, a pre-column 128, a column 129, a detector 130, and a workstation 100. The pumping apparatus 121 comprises two pistons 122 which reciprocate in pump chambers, respectively. The output of the first pump chamber is connected via a valve to the input of the second pump chamber. The pistons are driven by linear drives, e.g. ball-screw spindles. The stroke volume displaced by the piston is freely adjustable by corresponding control of the angle by which the shaft of the drive motor is rotated during a stroke cycle. The control circuitry 123 is operative to reduce the stroke volume when the flow rate which can be selected by user at the user interface is reduced, thus leading to reduced pulsations in the outflow of the pumping apparatus.
European Patent Application EP 05102533.6 relates to controlling piston movement of a metering device, whereby compressibility effects due to pressure variations are taken into account. The piston's velocity is set to a desired flow rate and the solvent pressure is monitored. In case of pressure variations, a corrective movement that corresponds to the pressure-induced variation of the solvent volume in the supply flow path is superposed on the regular piston movement.